Laser-Guided Spalling of Curved Semiconductor Layers
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Solution Overview
Problem
Conventional wafering methods for semiconductor materials, such as diamond or slurry-based wire sawing, result in material loss, surface damage, and require additional polishing and grinding steps, while spalling techniques face limitations in controlling wafer thickness and surface roughness due to Wallner lines.
Innovation Solution
A laser-assisted spalling method that uses short laser pulses with high numerical aperture to define a crack propagation plane, allowing for precise detachment of solid body layers by adjusting laser parameters based on material properties and doping levels, reducing surface roughness and material loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional wire sawing processes are used for wafering semiconductor materials, then cutting and separation can be achieved, but material loss occurs, surface roughness increases, and additional polishing and grinding steps are required
Solution Approach 1:
The patent replaces the mechanical wire sawing process with a laser-based spalling process. The laser creates a modification layer within the semiconductor crystal that guides crack propagation, enabling separation without mechanical contact. This substitution eliminates material loss from cutting gaps and surface damage from mechanical abrasion, achieving kerf-free wafering with superior surface quality.
Solution Approach 2:
The patent utilizes phase transitions in the semiconductor material through laser heating. The laser raises the temperature to create a modification layer that undergoes structural changes, enabling controlled crack propagation along crystal planes. This thermal phase transition approach allows precise detachment without mechanical force, eliminating both material loss and surface roughness.
2Loss of substance
If spalling processes are used to separate crystalline materials along crystal planes, then material loss is reduced, but Wallner lines are formed on the surface increasing roughness
Solution Approach 1:
The patent applies local quality by creating a focused laser modification layer at a specific depth within the crystal, precisely where the detachment plane is desired. The laser parameters (numerical aperture, pulse duration, energy density) are locally optimized to create modifications only in the target region, guiding cracks along the intended plane while leaving the surface quality unaffected. This localized approach eliminates Wallner lines by preventing uncontrolled crack propagation from the surface.
Solution Approach 2:
The patent performs preliminary laser modification of the crystal structure before crack propagation occurs. By pre creating the modification layer that defines the detachment plane, the crack is guided along the predetermined path rather than propagating uncontrollably from the surface. This preliminary structuring action eliminates the formation of Wallner lines by controlling the crack initiation and propagation mechanism.
3Manufacturing precision
If high numerical aperture optics are used with short laser pulses to define crack propagation plane, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent utilizes parameter changes in the laser system (pulse duration, numerical aperture, energy density, wavelength) to achieve precise control of the modification layer depth and crack propagation. By adjusting these parameters, the system can be optimized for different crystal materials and detachment depths. The parameter changes enable high precision without requiring mechanically complex positioning systems, as the focus depth is controlled optically rather than mechanically.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces surface roughness and material loss, enabling more efficient and precise detachment of semiconductor layers with improved surface quality, comparable to or exceeding traditional wire sawing processes.
Implementation Method 1
producing laser beams by means of the laser application device in order to produce respectively at least one modification
Implementation Method 2
Spalling was made possible by using differences in the thermal coefficients of expansion between a brittle material and a polymer adhering to the surface of the material
Implementation Method 3
a crack guiding region is predefined for guiding a crack for detaching a solid body portion
Implementation Method 4
Cooling of the associated materials below the glass transition temperature of the polymer induces stresses which result in the separation of material along a crack plane
Implementation Method 5
Since the laser photon energy is selected below the material band gap energy, the material is thus transparent to the laser radiation so that a deep penetration into the material can be achieved
Data Source
AI summary
A method for producing a solid body layer having a domed or curved shape at least in sections includes: irradiating a surface of the solid body by laser beams emitted from a laser application device to produce a modified region within the solid body that includes modifications having an extension in a longitudinal direction of the solid body, the longitudinal extension extending orthogonally to the irradiated solid body surface, wherein the modifications are configured to guide a crack for detaching the solid body layer upon application of an external force; and enlarging the extension of the modified region in the longitudinal direction to increase stress produced by the modified region in unmodified material of the solid body, wherein enlarging the extension of the modified region in the longitudinal direction increases the probability of spontaneous splitting of the solid body layer from the solid body without application of the external force.